This invention relates to systems and methods for increasing blood perfusion, e.g., in the treatment of myocardial infarction, strokes, and vascular diseases.
High frequency (5 mHz to 7 mHz) ultrasound has been widely used for diagnostic purposes. Potential therapeutic uses for ultrasound have also been more recently suggested. For example, it has been suggested that high power, lower frequency ultrasound can be focused upon a blood clot to cause it to break apart and dissolve. The interaction between lower frequency ultrasound in the presence of a thrombolytic agent has also been observed to assist in the breakdown or dissolution of thrombi. The effects of ultrasound upon enhanced blood perfusion have also been observed.
While the therapeutic potential of these uses for ultrasound has been recognized, their clinical promise has yet to be fully realized. Treatment modalities that can apply ultrasound in a therapeutic way are designed with the premise that they will be operated by trained medical personnel in a conventional fixed-site medical setting. They assume the presence of trained medical personnel in a non-mobile environment, where electrical service is always available. Still, people typically experience the effects of impaired blood perfusion suddenly in public and private settings. These people in need must be transported from the public or private settings to the fixed-site medical facility before ultrasonic treatment modalities can begin. Treatment time (which is often critical in the early stages of impaired blood perfusion) is lost as transportation occurs. Even within the fixed-site medical facility, people undergoing treatment need to be moved from one care unit to another. Ultrasonic treatment modalities must be suspended while the person is moved.
The invention provides systems and methods for applying ultrasound energy to a body region. The systems and methods provide an ultrasound applicator including a housing, an ultrasound transducer carried by the housing, and a chamber sized to hold an acoustic coupling media subject to a pressure in acoustic communication with the ultrasound transducer. The systems and methods generate electrical signals to operate the ultrasound transducer to output acoustic energy at a selected intensity level. The systems and methods sense at least one system parameter and compare the sensed system parameter to a desired level. The systems and methods vary the pressure in the chamber based, at least in part, upon the comparison.
In one embodiment, the system parameter includes impedance. In this arrangement, the systems and methods can vary pressure in the chamber based, at least in part, upon variance between the sensed impedance and a desired impedance level.
In one embodiment, the systems and methods select the desired level based upon the selected intensity level.
In one embodiment, the systems and methods vary pressure in the chamber to maintain an essentially constant acoustic output.
In one embodiment, the acoustic coupling media within the chamber conducts heat from the ultrasound transducer.